Dew
Dew is a fascinating atmospheric phenomenon, showcasing the
interplay of temperature, humidity, and surface conditions.
“Small drops of water that forms on plants, leaves, etc. during the
night.”
Formation of dew
Air holds moisture:
Cooling at night:
Condensation:
Dew formation: These tiny water droplets form on the cooled
surfaces, creating the dew we see in the morning.
Factors influencing dew formation: Clear, calm nights with high
humidity favor dew formation.
Dew Point above Freezing Point:
Fog
Fog forms when water vapor in the air condenses into tiny water
droplets. This typically happens when the air cools to its dew point,
the temperature at which the air can no longer hold all of its water
vapor. As the air cools, the water vapor condenses onto condensation
nuclei like dust or salt particles, forming visible fog.
Formation of Fog
1. Cooling: 2. Saturation: 3. Condensation Nuclei:
Different types of fog form under various conditions
Radiation Fog: Advection Fog: Upslope Fog: Steam Fog:
Frontal Fog:
Mist
Mist is formed when water vapor in the air condenses into tiny, visible
water droplets that remain suspended near the ground. This
condensation typically occurs when warm, moist air encounters a cooler
surface or air mass.
Key differences between mist and fog:
Visibility: Visibility in haze is 1,000 meters or more and in fog the
visibility is less than 1,000 meters.
Droplet size: 10-50 and 50-100 micrometer micrometers or more.
Density: Mist droplets are typically 10 to 50 micrometers (μm) and
fog generally considered to be 50 to 100 micrometers (μm) in
diameter or more.
Frost
Frost forms when water vapor in the air changes directly into ice
crystals on a surface, without first becoming liquid water. This
process, called deposition, happens when the temperature of a
surface is below the dew point of the surrounding air and the air
temperature is at or below freezing. Essentially, the water vapor
bypasses the liquid phase and transforms directly into ice crystals on
the surface.
Conditions conducive to frost formation
Clear skies:
Light winds:
High humidity:
Surface temperature:
Dew Point:
Deposition: This is the phase transition where water vapor turns
directly into ice. It's like the opposite of sublimation, where ice
turns directly into vapor.
Cool Surfaces:
Calm Conditions:
Types of Frost:
Radiation frost (or Hoarfrost): This is the most common type,
forming on the ground or exposed objects on clear, still nights when
heat radiates away rapidly.
Advection frost: This forms when cold wind blows across surfaces
that are below freezing, resulting in small ice spikes.
Window frost: This forms on glass panes when there's a significant
temperature difference between the warm, moist air inside and the
cold air outside.
Rime: This forms quickly in very cold, humid, and windy conditions,
often appearing more icy and solid than other frost types.
Clouds
Clouds are visible masses of tiny water droplets or ice crystals
suspended in the atmosphere that play a vital role in Earth's
weather.
The formation of clouds involves several steps:
1. Evaporation: The process begins with water evaporating from
bodies of water like oceans, rivers, and lakes, as well as from land
surfaces and plants. This evaporated water becomes water vapor, a
gas, and rises into the atmosphere.
2. Rising air: Heating of the ground (convection), air being forced
upwards by mountains (orographic lifting), or air masses colliding
and being pushed upwards (convergence). .
3. Cooling of air: As air ascends, it cools, reducing its capacity to retain
moisture.
4. Condensation: When the air cools to its dew point, water vapor
condenses around tiny particles called condensation nuclei.
5. Cloud formation: The accumulation of these droplets or ice crystals
forms a visible cloud, with type and appearance influenced by
altitude, temperature, and humidity.
6. Growth and development: Clouds can grow through further
condensation or droplet merging, potentially leading to
precipitation.
Dew point: The temperature at which condensation begins.
Adiabatic cooling: The primary cause of air cooling that drives cloud
formation.
